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I'm confused in differentiating the OSI Model and TCP/IP suite. As per my knowledge. OSI is a structure on top of which Networks are built and TCP/IP is the suite of protocols that operate on these 7 layers of OSI. Correct me if I'm wrong. Also, is TCP/IP a replacement to OSI and is used IN PLACE of OSI? or both these work COLLECTIVELY to form the Network? any good source to clarify my confusion will be appreciated.

Thanks.

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This sounds like it'd be better asked on serverfault or something as it doesn't strictly relate to programmers. –  Doug T. Feb 4 '12 at 12:58

2 Answers 2

up vote 4 down vote accepted

The OSI stack is a rather theoretical model (and standard) for networking layers, but it has little practical relevance and mainly survives as a subject of CS classes.

TCP/IP is a suite of concrete networking protocols that have seen overwhelming adoption on the internet. It roughly maps to the layers 3 and 4 in the OSI model.

Concrete protocols rarely fit the OSI model perfectly, e.g. layers 1 and 2 are usually combined, as are layers 6 and 7 (often also 5).

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So shall I consider both OSI Model and TCP/IP two different stacks built for same purpose, but TCP/IP adopted widely while OSI remained something to be studied in CS and not in use in real world anymore? –  Kush Feb 5 '12 at 19:33
    
@Kush: basically yes, though the other big difference is that TCP/IP is a working implementation and OSI only an abstract model you cannot actually use. –  Michael Borgwardt Feb 6 '12 at 8:23

The OSI model is a networking model. DECNet has evolved from a 4 layer model to the OSI model.

TCP/IP is a different model and implementation of a network stack.

As they are different models and implementations, there is normally no question of interoperation between the two. If this needs to be done, a network bridge might be used.

In terms of modelling some of the OSI layers can be loosely mapped to the TCP/IP layers, though it is more granular so several OSI layers sometimes map to a single TCP/IP layer.

See this short article comparing the two architectures.

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I'm not sure what you mean by "never been implemented". There are technologies that implement each of the 7 layers as defined in the OSI model. The TCP/IP model is just another way of looking at networking. Both define networking, from the physical connections between two networked devices to applications that transmit data over that link. –  Thomas Owens Feb 4 '12 at 10:59
    
@ThomasOwens - I mean a whole network stack that is directly modelled on the OSI model. I don't know of one. Yes, there are individual parts, but now a whole, as far as I know. –  Oded Feb 4 '12 at 11:04
    
@Oded, I think, but may be mistaken, that DECnet had evolved in an OSI stack. Decnet is no more really relevant nowadays, but you can still think trace, X Windows has still syntax supporting DECnet for instance. –  AProgrammer Feb 4 '12 at 11:22
    
@AProgrammer - Looks like you are right. It has evolved into one: en.wikipedia.org/wiki/DECnet –  Oded Feb 4 '12 at 11:23
    
There certainly used to be "directly inspired by OSI" network stacks. The IS-IS routing protocol is a multi-protocol IGP carried over OSI. –  Vatine Feb 4 '12 at 11:45

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